If you want to understand other people, think of them as extremely selfish. Everybody is, even you and me. Every little thing we do is, eventually, for no one else than ourselves. Just think about it, let it sink in, and remember the last thing you did for somebody else. Why did you do it? Why did you really do it?

You just send a card to a lonely elderly person? Congratulations, you just bought yourself some feel-good hormones.

You lend a ladder to a neighbour who couldn't reach the grapevine running alongside his house? Congratulations, you just satisfied you're nosy instinct and had a good look around their house.

You gave a tip after a not that great dinner in a restaurant? Great, you don't want to seem like a dick to your guests. (If you gave a big tip, you're just gloating/trying to impress)

You're a politician and are trying to make this world a better place? Oh, don't even get me started.

Everything we do, we do to make our lives better, make ourselves feel better, and make ourselves seem better. The only reason we started roaming around together was so we could protect each other during the night or could hunt down a big animal (ever tried to hunt down a mammoth on your own?) We did it to make our lives easier and safer.
These days we live in cities, all clustered together, not because it's such a nice place to be, but because we don't want to travel to get to work and get our groceries. We want a comfortable life without too much of a hassle and cities are just great for that.

We unconsciously choose to do things, big and small, all in the name of Selfishness. Sometimes we don't even know it ourselves until you start and think about it. We always did, and always will. It's the core of who we are.

But don't be so down on the world right now, it has always been this way, you just never cared enough to think about it, but you probably always knew. And it does explain a lot of stupid things people do. Oh well...

Oh, and one tiny thing, never be as blunt as to tell someone they're only doing it out of selfishness, because they might not like you anymore, which is a bad thing, for you.